The present invention generally relates to optical transmission networks and more particularly to the establishment of dedicated LAN connections in optical transmission networks.
In optical transmission networks, information is transmitted between network elements (NEs) via optical fibers. As is well known, the majority of the transmission capacity available in each fiber is typically used for transporting client information (hereinafter referred to as payload) while some capacity (hereinafter referred to as overhead) is set aside for transmission management and control.
In the majority of optical transmission networks, it is common to provision dedicated connections between NEs which do not use any of the optical fiber capacity used for payload transmissions. These connections are highly desirable because they can provide some additional and separate connectivity between NEs without using any transport capacity which could otherwise serve for transmitting payload information and generate revenues.
Dedicated connections are often provisioned in optical transmission networks to provide remote access to or interconnect local area networks (LANs). For example, dedicated connections will be established between NEs of an optical transmission network where different NEs are located in close proximity of separate LANs or where a user connected to one NE wishes to access a LAN located in proximity of another NE. By using dedicated connections, LANs can be interconnected or remotely accessed through an optical transmission network without using any of the payload capacity available therein.
Dedicated connections in an optical transmission network can also be used to monitor equipment for maintenance, administration, provisioning or simply to monitor data transmissions. Typically, the monitoring is performed remotely from a central monitoring unit installed in proximity to a particular NE, and connected to other NEs in the network via dedicated monitoring connections.
Presently, various methods are used to provide dedicated connectivity between NEs of an optical transmission network. However, these methods all present a number of disadvantages.
Considering in particular the equipment monitoring usage, one traditional approach is to use a standard telephone connection between the monitoring unit and each NE in the network where equipment is to be monitored. In this approach, each telephone connection is terminated at its ends with a respective modem. At each NE, the modem terminating the telephone connection is connected directly to the monitored equipment by way of a serial connection such as, for example, RS-232. For NEs with multiple pieces of equipment to monitor, a pool of modems connected in parallel must be used where each modem provides a connection between the monitoring unit and a particular device or element to monitor in a one to one (1:1) arrangement.
Apart from the inherent bandwidth restrictions of conventional telephone lines, this approach has a number of drawbacks. First, telephone network connectivity is required at both the monitoring site and each of the NEs where equipment is to be monitored. For NEs with many devices or elements to monitor where, as noted above, a large number of modems is required, this approach could be quite prohibitive, particularly for NEs in remote areas.
In addition to being prohibitive, this method increases the complexity of the monitoring equipment. More specifically, with the need to establish at least one telephone connection and use at least one modem at each NE where equipment is to be monitored, data collection cannot be easily automated unless a sophisticated-monitoring unit is used. Further, because the modems and telephone connections used at each NE are external to the optical transmission network, they must be managed separately. Apart from the obvious resulting high cost, maintaining a separate network of telephone connections and modems would also have a considerable impact on the overall complexity of the monitoring equipment.
Another conventional method used to provide dedicated connectivity for remotely monitoring equipment at NEs without using the available network capacity consists of deploying a dedicated network of data connections linking the monitoring unit with each monitored NE site. According to this method, each data network connection is terminated at its ends with a respective bridge. At each NE, the bridge terminating the network connection is connected directly to the monitored equipment by way of a multi-access link such as Ethernet. Similarly to the telephone method described above where at each NE, modems must be connected to the monitored equipment in a 1:1 configuration, a bridge can also be connected in a 1:1 arrangement. In contrast however, bridges can also be connected in a 1:N arrangement if a large number of devices must be monitored.
An obvious advantage of dedicated data network connections over telephone lines is that the capacity provided by data network connections is considerably higher and with possible 1:1 or 1:N connection arrangements, the connectivity provided at each NE is more flexible. However, despite offering a higher transmission capacity and a more flexible connectivity at each NE, this approach requires that a separate data network be deployed and maintained separately from the optical transmission network. Similarly to the telephone line approach described above, the provisioning and maintenance of a separate data network substantially increases the overall cost and complexity of the optical transmission network.
In synchronous optical networks (SONET), another conventional method for remotely monitoring equipment without using any of the available payload transport capacity consists of using an audio channel in the SONET overhead. This channel typically referred to as the orderwire (OW) channel is normally provisioned for voice communications in the network. According to this method however, the OW channel is provisioned instead to establish a monitoring connection between NEs and a monitoring unit.
According to this method, the monitoring unit is connected to a nearby NE with a modem and a telephone line to access to OW channel. At NEs with equipment to monitor, a telephone line terminated with a modem is also used to connect to the OW channel. For NEs with multiple pieces of equipment to monitor, a pool of modems connected in parallel must also be used where each modem provides a connection between the monitoring unit and a particular device or element to monitor.
The main benefit of this approach is that it does not require a separate telephone network. However, because modems and telephones lines are still necessary, the disadvantages associated with their use also apply to this method. This includes low capacity, limited connection flexibility at the NEs (limited to 1:1 configurations and not 1:N configurations), complex data collection at the monitoring unit and the need to manage a network of modems separately from the optical transmission network.
Therefore, in view of the shortcomings of conventional dedicated connection schemes, it would be desirable to provide optical transmission networks with dedicated connections between NEs which are cost-effective, simple and can offer increased capacity, flexible connectivity without the need for managing or maintaining external network components.
The present invention provides a method and apparatus for establishing dedicated local area network (LAN) connectivity between network elements (NEs) in an optical transmission network without using any of the payload transport capacity available.
In order to provision dedicated LAN connections in an optical transmission network without using the available payload transport capacity, the invention reallocates overhead functionality to provide dedicated bandwidth between NEs. At each NE, a respective LAN interface unit provides access to this dedicated bandwidth and allows the NEs or LAN networks or devices connected thereto such as personal computers (PCs), servers and monitoring equipment to communicate without consuming any payload transport capacity available in the network.
According to a broad aspect, the invention provides a method of transmitting LAN data in an optical transmission network wherein information is transmitting frames, each frame containing a first plurality of bytes for transmitting payload data and a second plurality of bytes for transmitting overhead data, the method comprising allocating in each frame one or more bytes of the second plurality of bytes for LAN data transmissions, for each LAN data transmission, transmitting frames with LAN data in the one or more allocated bytes until the LAN data transmission is complete.
According to another broad aspect, the invention provides an optical transmission network formed of multiple NEs interconnected with optical links where each link has a defined payload transmission capacity allocated for payload data transmissions and a defined overhead transmission capacity allocated for overhead data transmissions of which a portion is reallocated for LAN data transmissions, the optical transmission network comprising at each NE a LAN interface connected to receive LAN data from one or more LAN devices for transmission in the reallocated portion of the overhead transmission capacity and an optical transmitter connected to the LAN interface and operable to transmit the received LAN data using the reallocated portion of the overhead transmission capacity.
According to yet another broad aspect, the invention provides an apparatus for a first NE in an optical transmission network for transmitting LAN data to a second NE via an optical link interconnecting the first and second NE wherein the optical link has a defined payload transmission capacity allocated for payload data transmissions and a defined overhead transmission capacity allocated for overhead data transmissions of which a portion is reallocated for LAN data transmissions, the apparatus including a LAN interface connected to receive LAN data for transmission with the reallocated portion of the overhead transmission capacity and an optical transmitter connected to the LAN interface and operable to transmit the received LAN data using the reallocated portion of the overhead transmission capacity.
According to yet another broad aspect, the invention provides a LAN interface connecting a LAN device to a NE in an optical transmission network of a defined payload transmission capacity allocated for payload data transmissions and a defined overhead transmission capacity allocated for overhead data transmissions of which a portion is reallocated for LAN data transmissions, the LAN interface being operable to receive LAN data from the LAN device and process the LAN data received for transmission using the reallocated portion of the overhead transmission capacity. Preferably, the reallocated portion can either be an optical channel such as the optical service channel (OSC) or overhead bytes in an optical channel. In the latter case, the overhead bytes could be one or more overhead bytes.
The invention can be incorporated in any optical transmission network topology or configuration such as for example, synchronous optical networks (SONET) or optical transport networks (OTN) where it is desirable to establish dedicated connections between NEs without using any of the payload transport capacity available.
In a preferred embodiment, the invention is used to provide dedicated layer 2 Ethernet connectivity between NEs in a SONET network. In order to provide this Ethernet connectivity, the invention uses F1 bytes in the SONET overhead to establish dedicated bandwidth for Ethernet communications between NEs. When the SONET overhead is not visible, it is possible to use other overhead functionality to establish dedicated bandwidth. In another preferred embodiment, an optical service channel is used to provide this dedicated bandwidth. In both embodiments, an Ethernet wayside (EW) unit is used at each NE to provide access to this dedicated bandwidth. The EW unit can be used to attach multiple Ethernet devices or networks.
By using overhead bytes (e.g. F1 bytes) or optical channels which are conventionally allocated for overhead, the invention can be used to support various LAN communications across the NEs without using any of the payload bandwidth available. For example, the dedicated bandwidth could be used for software download of loads to each NE. Alternatively, a network administrator at a monitoring unit could remotely monitor equipment at or in proximity of the NEs in the network without consuming any of the payload transmission capacity available and adversely affect transport revenues.
Another advantage of the invention is that the dedicated LAN connections provided by the present invention can provide in excess of 10 megabits per second of transport capacity. In addition, the dedicated LAN connections are provisioned internally to the optical transmission network therefore eliminating the need for deploying and maintaining any additional telephone or data network external to the optical transmission network. Therefore, the overall cost of providing dedicated connections in an optical transmission network is considerably reduced.
Yet another advantage of the present invention is that multiple LAN devices can be connected at each NE via a single LAN interface unit (e.g. a EW unit). With this ability, the invention can advantageously be used to establish point-to-point or point-to-multipoint LAN connections between NEs of an optical transmission network. In addition to equipment monitoring, these point-to-point or point-to-multipoint LAN connections can also be used for LAN applications such as for example, connectivity between LANs or as a further example, remote access by one or more users to a LAN.